(CNN) — James Holmes, the suspect in the shooting at a screening of the newest Batman movie, had colored his hair red and told police he was “the Joker,” according to a federal law enforcement source with knowledge of the investigation.

Police have not yet released Holmes’ mug shot.

Nuggets of information about the alleged 24-year-old gunman began emerging Friday, but what may have motivated him remain elusive.

Eyewitness accounts describe the shooter who entered a packed movie theater as being dressed all in black, a bulletproof vest around his frame, and what appeared to be a gas mask.

The witnesses saw the attacker throw two canisters — possibly tear gas — before opening fire on the crowd. He did not say a word, one witness said.

Police arrested Holmes in a rear parking lot of the theater. He did not resist.

According to Aurora police chief Dan Oates, Holmes also wired his apartment with traps for authorities.

“It’s booby trapped with various incendiary and chemical devices and trip wires,” Oates said, adding that it could take days to work through the apartment safely.

Five buildings around Holmes’ Aurora apartment were evacuated, Oates said.

It turns out that Holmes, who has roots in San Diego, was student at the University of Colorado School of Medicine in Aurora. He was in the process of withdrawing at the time of the shooting, university officials said. He was a doctoral student in the neuroscience program.

A college syllabus that lists Holmes as a student shows that he may have taken a class in which he studied topics as diverse as substance abuse, schizophrenia, depression and other disorders.

According to the document, he was supposed to have made a presentation in May about microRNA biomarkers.

Police also revealed that Holmes lived in a small apartment on Paris Street in Aurora, in Apartment 10.

Donald Robert Davis, 52, lived in Apartment 10 for about two years before moving out about a year ago. He described it as an approximately 850-square-foot, one-bedroom apartment with one bathroom for which he paid $525 per month, not including utilities.

On Friday, authorities evacuated the entire apartment building after Holmes made a “statement about explosives” to police, Chief Daniel Oates said.

A neighbor who lives one floor underneath Holmes, Tori Lynn Everhart, described the apartments this way: “It’s not like true ghetto. It’s not the safest neighborhood, but it’s definitely improving.”

Large chunks of Holmes’ past prior to medical school remain unknown.

Meanwhile in San Diego, his family released a statement saying they were still trying to process the news.

“Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved,” the Holmes family said, without giving any information about the suspected shooter.

The Poway Unified School District in San Diego confirmed that James Holmes graduated from Westview High School in 2006.

But his friends, his interests and his personality remained a mystery.